This invention relates generally to sealing and triggering arrangements for oscilloscopes, and in particular to a system for analyzing input signals using amplitude and time histograms to establish vertical sensitivity, time base setting, and triggering levels for oscilloscopes to provide stable, viewable displays.
Typical digital oscilloscopes rely on the user to manually adjust vertical and horizontal scale factors, and to adjust the triggering level to achieve stable triggering. More sophisticated oscilloscopes utilize digital comparators to detect peak amplitude values of input signals automatically to establish vertical sensitivity and level-crossing trigger detection automatically to establish a time base setting as well as a triggered display.
Achieving stable triggering has always been one of the more difficult tasks in operating an oscilloscope. In analog oscilloscopes, a trigger comparator issues trigger signals to start an associated time base sweep when an input signal matches a voltage level adjusted arbitrarily by a user, and often the precise triggering point is difficult to ascertain. In digital oscilloscopes, issuance of a valid trigger signal often is used to stop digital acquisition of an input signal in a so-called post-trigger mode, freezing the contents of an associated waveform memory so that a later reconstructed waveform display will show the user events leading up to the triggering event. Thus, establishing a set of conditions upon which a valid trigger will be issued can be complicated, even for experienced users. Accordingly, many attempts have been made to provide automatic triggering to relieve the user of this often frustrating task.
Many users are only interested in a stable image of an input signal to see whether or not something is wrong with the shape of the signal. For these users, operating the instrument is only a bothersome necessity. As oscilloscopes are being simplified and designed for use by lesser experienced personnel, a simple and inexpensive method of establishing automatic vertical sensitivity, time base setting, and triggering is desired.